Case Study

Georgia Tech Research Instituteresearchers are casting new light on the disinfection of water used in
food processing. They have developed a method that performs better and
is less costly than existing techniques.

Like
current technologies, the new Advanced Disinfection Technology System
relies on ultraviolet (UV) radiation to eliminate molds, viruses and
bacteria. But the new system handles water more efficiently and thus
improves the overall effectiveness of the disinfection process.

"We're
creating a mixing pattern to ensure that every particle of water is
equally exposed to the (UV) lamp," says John Pierson, a senior research
engineer at the Georgia Tech Research Institute and co-principal investigator. "By doing a better job of mixing the water, you get better disinfection."

Federal regulations
require the disinfection of water used in food processing before it can
be reused. In many cases, the lack of cost-effective disinfection means
water is used only once and then discarded. When a disinfection system
is used, the process is not always effective.

Most existing systems pump
water through pipes lined with dozens of UV lamps. The lamps tend to
foul quickly, reducing their effectiveness and requiring ongoing
cleaning and replacement. More important, UV light has little
penetrating power - just about an inch - so used water must be run
through long pipes to increase the likelihood that UV light will
contact enough of the liquid to affect the microorganisms it carries.

"Water right up against
the lamp gets treated, and water farther away gets treated less - or
maybe not treated at all," explains Pierson, who is collaborating on
the advanced disinfection system with Larry Forney, project director
and an associate professor of chemical engineering in the School of Chemical Engineering at Georgia Tech.

The heart of the new advanced system is a pair of cylinders, one inside
the other. The smaller cylinder rotates inside the stationary outer
cylinder while water is pumped through the gap separating the two.

Inside the gap, the cylinder rotation causes water to churn and tumble
in a well-documented phenomenon called a Taylor vortex. It's actually a
number of vortices, which mix water with light shining from four UV
lamps embedded in the outside cylinder wall.

UV light penetrates the water thoroughly, so no additional cycles
through the system are necessary. Fewer UV lights are required compared
to conventional systems, thus saving energy.

"Even if the fluid absorbs radiation, which would normally limit light
penetration and thus the effectiveness of conventional UV reactors, the
vortex motion in the new design continuously exposes fresh fluid to the
radiation surface," Forney explains. "You bring the fluid in contact
with just a few lamps in a repetitive basis."

The vortex motion also keeps the lamps free of material buildup.

The device is mechanically simple. Its low rate of revolution - about
one cycle per second - means no bearings or special seals are required,
Forney adds.

The process was designed for recycling water from fruit and vegetable
washing at food-processing plants, but it could be applied in other
industrial processes.

"We
think it could be useful for a number of water-treatment situations
ranging from storm-water runoff to bottle washing to certain
industrial-process water recycling applications," Pierson says. "It
fits any application where you could use disinfected water rather than
potable water, which would cut down on water use generally and conserve
potable water in particular."

The disinfection process developed by Forney and Pierson may find uses
far beyond the project's original scope. Virtually anything that flows
can run through the system, allowing for applications in the soft drink
industry, brewing, dairy products and fruit juice processing. It would
work for any kind of fluid for which there are concerns about the
existence of pathogens, Forney says. A non-thermal procedure, it could
even supplant pasteurization, which is expensive, changes the taste and
consumes a lot of energy, he adds.

A variation of the device could even be developed for swimming pools as a non-chemical alternative to keeping water germ-free.

"If you were able to pass pool water through a UV reactor successfully,
it would feel like normal water," Forney says. "It would have no taste
and wouldn't be irritating to your mouth, eyes and lungs."

Preliminary work with the new lab-scale UV disinfection device shows a
reduction in the concentration of viable pathogens by a factor of more
than 200, compared to existing technology with the same UV dosage,
according to Carolyn Goodridge, a visiting postdoctoral fellow and
member of the research team.

"We're also beginning to work with certain kinds of fluids, such as
fruit juices, that absorb lots of radiation to see what effect our
device has on the inactivation of pathogens in that kind of
environment," Forney adds.

The research is sponsored by the state of Georgia through its Traditional Industries Program
(TIP), a public-private partnership created by the General Assembly in
1994 to bring university-based research to bear on challenges faced by
industry. TIP research and development for the food processing industry
is coordinated through the Food Processing Advisory Council. In
addition to the food processing industry, TIP also addresses
industrywide issues in Georgia's textile and carpet, and pulp and paper
sectors.